Vertical beam steering antenna system



May 5; 1970 JEA. GREEN AL 3,510,876

VERTICAL BEAM STEERING ANTENNA SYSTEM Filed June 29, 1967 3 Sheets-Sheet 1 n 0) k qlx 2 Ik AGENT My 5, "1970 J. A. GREEN ET AL. 3,510,876

VERTICAL BEAM STEERING ANTENNA SYSTEM JOSEPH A. GREEN BY R/CHARO 0. WRIGHT AGENT May 5, 19170 .1. A. GREEN ETAL. 3,510,876

VERTICAL BEAM STEERING ANTENNA SYSTEM 90 n@ 90o .60o (Ream/MMU #Rear/Nc Y: Mang/s Parque/vcr: voo/vc/S 30 ae'Ql/avcw/oooMq/s Joss/wf am @Ref/v U.S. Cl. 343-798 i Ulnitedl States PatentV O ABSTRACT F THE DISCLOSURE An antenna system for providing vertical beam steering `which is substantially frequency insensitive utilizing no dissipative elements, thereby achieving a higher ethciency. The antenna system comprises at least one pair of angularly` oriented bisecting antennas inclined at substantially equal angles with respect to the ground plane. This conguration simulates virtual horizontal and vertical radiators when signals which are complex conjugates of each other which are applied to the angularly oriented antennas to provide the d esired vertical beam steering.

The invention herein described was made in the course of or under a contract with the Department of the Navy, U.S. Government.

FIELD OF THE INVENTION This inventionrelates to vertically steered antenna systems and more particularly to a vertically steered antenna system which is substantially frequency insensitive and which provides improved efficiency over the systems known in the art.

BRIEF DESCRIPTION OF THE PRIOR ART Most prior art antenna systems for providing vertical beam steering are frequency sensitive and are therefore undesirable for use in broad-band systems. One known antenna system for providing substantially frequencyindependent vertical beam steering utilizes a vertical array of horizontally polarized antenna elements which are fed through pairs of cables and appropriate summing networks associated with each element to assure the proper excitation. This type of array provides substantial frequency independence but a practical objection to this steering method results from the necessarily inefficient operation of the summing networks, particularly when used at low frequencies and for small steering angles. In such a case, the summing networks may be required to dissipate more power than is actually radiated by the antenna array itself in order to obtain the desired radiation pattern. y

Another antenna system presently known in the art utilizes adjustable phase shifters which must be readjusted each time the frequency is changed in order to maintain aconstant vertical steering angle. While this system is operable over a wide range of frequencies, it is not frequency insensitive without the making of later readjustments.

Therefore, the main object of this invention is to provide a substantially frequency independent vertical beam steering antenna system which provides improved efficiency over those known in the art.

A further object of this invention is to provide such an antenna system which requires no adjustments to maintain the vertical steer angle constant when the frequency is changed.

A still further object of this invention is to provide such an antenna system wherein no dissipative elements are utilized.

f V' 3,510,876 .ce Patented May 5, 1970 SUMMARY OF THE INVENTION According to this invention, a vertical beam steering antenna system includes a ground plane at least one pair of angularly oriented antennas mounted above said ground plane and which are inclined at substantially equal angles with respect to said ground plane. Further provided is an input source for providing the respective inclined antennas with respective signals which are the complex conjugates of each other referred to a predetermined point on saidV ground plane, saidV inclined antennas simulating virtual horizontal and vertical radiators.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an illustration of a preferred antenna array according to the invention;

FIG. 2 is a more detailed illustration of a portion of the array of FIG. 1 to more clearly illustrate the concept of the invention;

FIG. 3 illustrates a typical feed arrangement for the antenna array of FIGURE l;

FIG. 4 is an illustration of an unrealizable antenna array which is useful for analyzing the array according to the invention;

FIG. 5 illustrates the experimentally determined vertical response of the array of FIG. 1 for a vertical steer angle of 0 degree; and

'.FIG. 6 illustrates the experimentally determined vertical response of the array of FIG. 1 for a vertical steer angle of 20 degrees.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there is shown one embodiment of an antenna array according to this invention which comprises four sets, 1, 2, 3 and 4, of orthogonally oriented pairs of dipole antenna elements mounted above ground plane 6 in a common vertical plane on support member S. In appropriate circumstances ground plane 6 may merely comprise the earths surface. The lower set of elements 1 is mounted at a height h1 above ground plane 6 and comprises dipole elements 7-8 aud 9-10. The second set of elements 2 is mounted at a height l12 above ground plane 6 and comprises dipole elements 11-12 and 13-14. Likewise, the third set 3 is mounted at a height h3 and comprises dipole elements 1546 and 17-18 and the fourth set 4 is mounted at a height h4 and comprises dipole elements 19-20 and 21-22. In this embodiment each of the dipole elements 7-22 are triangularly shaped. This is merely a design preference to obtain desired performance characteristics and it should be clear that any other element shape may be used, depending upon the system application.

When properly fed, i.e. by a feed system such as that shown in FIG. 3 which is described hereinbelow, each of the four sets of antenna elements 1, 2, 3 and 4, provides a virtual horizontal and a virtual vertical radiating element (see FIG. 2). To provide this result, a first signal is applied to one pair of elements for each set, Le., elements 7-8 of set 1, directly through direct-ray delays and a second signal which is the complex conjugate of the first signal (referred to the point on the ground plane 6 immediately below the antenna elements) is applied to the other pair of elements for each set, i.e., elements 9-10 of set 1, directly through ground-reflected ray delays. Thereby, each set of elements, i.e., radiating elements 7-8 and 9-10 of set 1 behave as a spacial summing circuit and provide virtual horizontal and vertical radiators each having a phase center located at the intersection of the two orthogonally inclined radiators.

FIG. 2 illustrates schematically the antenna elements (real and virtual) of a typical set of elements, such as set 1 of FIGURE 1. The real antenna elements are represented by the lines designated 23-24 and 25-26. Elements 23 and 24 taken together form a dipole element, for example, and comprise a first antenna oriented at a 45 angle with respect to the horizontal. Elements 2S and 26 taken together also form a dipole element, for example, and comprise a second antenna also oriented at an angle of 45 with respect to the horizontal. The first and second antennas bisect each other and are orthogonally oriented with respect to each other. This configuration simulates virtual antennas 27 (vertical) and 28 (horizontal) when fed With the appropriate signals according to the invention. In FIG. 2 the antenna elements are shown as straight lines merely for ease of illustration and it should be clear that any desired type of element may beVY used to provide the desired result. It is further pointed out thatY while 1t is preferred that the first and second antennas be orthogonally oriented with respect to each other, the system will also operate with other angular orientations. In this case modifications to the feed arrangement may be necessary and the radiation characteristics of the system may be somewhat altered.

By proper design of the elements and feed networks, the far-field radiation pattern provided by the virtual horizontal antenna 28 shown in FIG. 2 would be identical to that which is provided by the horizontal radiating elements in antenna arrays known in the art. The far-field radiation pattern having a maximum at the vertical angle is denoted by the equation:

where A1=amplitude of the field of the ith element; h1=height of the ith element above the ground plane; k=wavelength at the operating frequency; and a=desired vertical steer angle.

This equation is given in Reference Data for Radio Engineers published 'by International Telephone and Telegraph Corporation, fourth edition, page 697. It should be noted that the equation in the reference gives the height h1 in degrees, whereby in this description the height h is given in radians. This accounts for the 21r/)\ which appears in the above equation.

Power associated with the out of phase component of the radiation previously dissipated in the prior art arrays as heat in summing circuits or the like, is now radiated, according to this invention, in a vertically polarized mode by means of the virtual vertical antenna 27 of FIG. 2. The far-field radiation pattern of the virtual vertical antenna 27 is given by:

The equation for Amm.) is essentially given on page 692 of the above-cited reference with reference to configuration B. `In the subject case the virtual vertical antenna 27 prevents an equivalent situation with the ground plane 6 being located in a vertical plane midway between the antennas A shown on page 692 of the reference. This accounts for quantity the S/2 in the reference equation, which is the spacing between the two elements in degrees. The virtual vertical antenna 27 electrically looks like the configuration B of the reference. Note that the vertically polarized mode is also directed in the far field to the same vertical angle a as was the horizontally polarized mode and that the cophasal combination of the direct and ground-reflected components produces a radiation pattern maximum at the vertical angle in the far field.

It is pointed out that only delay elements are required to generate the conjugate signals required for feeding the antenna array and that no dissipative circuit elements are needed. Therefore, substantially all the power transmitted to the real dipole elements 7422 according to the invention can be radiated in the .ideal situation. Since the direct and ground-refiected rays are each synthesized by means of time delays, the vertical angle a will remain 4 substantially constant as the frequency is varied for a semi-infinite antenna array and will only vary slightly for an antenna array of practical size.

Referring to FIG. 3, a preferred feed arrangement for the antenna array of FIG. 1 includes an input signal source 30 coupled to a power splitter 31. The output of the power splitter 31 is coupled to the input of a second power splitter 32 via a delay element 33 and to the input of a third power splitter 42 directly. The outputs of the power splitter 32 are fed to pairs of antenna elements 9-10, 13-14 and 17-18 of the array of FIG. l via respective delay elements 34, 35 and 36. An output of power splitter 32 is also fed to element pair 21-22 directly. The outputs of power splitter 42 are applied to pairs of antenna elements 11-12, 15-16 and 19h-20 of Vthe array of FIG. 1 via respective delay elements 37, 38 and 39. An output of power splitter 42 is also fed directly to element pair 7-8. Y

Note that mathematically, negative delays are necessary to provide conjugate phase excitation for the element pairs. But, since such negtaive delays cannot exist in practice, a constant positive delay was added to all of the elements, which constant delay equals the maximum value of the required negative delay. This merely produces an absolute phase shift of the radiated pattern without disturbing the component-phasor interrelationships and the manner in which they vary with vertical steer angle. Thus, the array pattern itself is unchanged due to the addition of the constant delay in series with all of the elements. By means of the above apparatus the two element pairs in each set of antenna elements receives respective signals which are the complex conjugates of each other referred to the sub-array point on the ground plane 6, and thereby produces the desired radiation pattern according to the given equations.

The principles of the above-described antenna array may be described in an alternate andequally valid manner that yields, perhaps, a better insight into certain aspects of the substantially lossless steering method disclosed herein. Such a decription appears below.

Referring now to FIG. 4, there is shown an unrealizable antenna array in` which the driven antenna elements and their ground reflected images are shown. Such a configuration may lbe resolved into two, orthogonally polarized ($45 degrees with respect to the horizontal ground plane 6) component arrays. Half of each array is composed of two of the real radiating elements A1, A2, B1 and B2 and the other half is composed of two of the ground reflected, virtual radiating elements A1, A2, B'1 and B'z. If real element pairs A1-B1 and A2-B2 are driven with currents that are complex conjugates of each other when referred to a phase-reference point located at the intersection of the array with the ground plane `6 and with phase variations linearly related to the height h of each set of antennas from the ground plane 6, it follows that one of the copolarized arrays consisting of, for example, radiating elements A2, A1, B1, BZ will ygenerate a beam with a maximum sensitivity directed to an angle -I-a above the horizon. The other array, consisting of co-polarized elements A2, A1, B1, B2 will synthesize a beam directed to an angle a referred to the ground plane 6. But, since the virtual elements do not physically exist, the -a maximum, itself, also does not exist, and only that portion of the radiation pattern associated with the a beam that enters the positive angle region is significant.

It is apparent from the discussion of the array of FIG. 4, that in the vicinity of the maximum at -i-a, the resultant polarization will 'be linear and inclined to approximately 45 degrees with respect to the horizontal ground plane 6, for moderate vertical steer angles and for an aperture large enough so that the side lobe levels associated with -the -a maximum are negligible in vicinity of -i-a.

Referring to FIG. 5, there is shown the experimentally determined response of the array of FIG. 1 driven by the feed arrangement of FIG. 3 at threedifferent frequencies for zero degree vertical steer angles. Note that the radiation pattern maximum does not actually occur at zero degreesbecause of the effect of the finite conductivity and `the finite extent of the ground plane 6 which preferably comprises a copper or other conducting counterpoise.

FIG. 6 illustrates the response of the antenna system of FIGS. l and 3 at three different frequencies when the proper values of delays are inserted so as to steer the pattern to approximately a 20 degree vertical angle. Note that in the radiation patterns of FIGS. and 6 the angle of the radiation maximum is substantially invariant with frequency. Y Y Y It is pointed out here, that the mixed polarization characteristics of the resulting antenna array according to the invention, should not prove to be a significant impediment in its application to many problems involving ionispheric propagation. It has been found in practice that such effects are not serious for most applications.

In a reduced scale model of an H F. antenna system according to FIGS. 1 and 3 operating at a frequency of 1000 mHz., the following parameter values were calculated for a vertical steer angle of 10:

Fora vertical steer` angle of the heights ily-h4 remain the same but the required delay values are as follows:

Delay 36=Delay E37-:74.88 Delay 35=Delay 38=l50.12 Delay 34=Delay 39=225.36 Delay. 33=299 52 ,In both of the a'bove cases the additional delay contributed 'by cables in the distribution system was assumed to be substantially equal and constant for each feed line. The value` of the delays 36 and 37 were computed from the followingwell known equation:

Note that the other values of delay are multiples of delay 36.

While` we have described above the principles of our invention in connection with specific apparatus it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the` accompanying claims.

We claim:

1. A vertical beam steering antenna system comprising:

a ground plane;

at least one set of antennas mounted above said ground plane, each said set including first and second angularly oriented antennas, each said antenna being inclined at substantially equal angles with respect to said ground plane; and

means coupled to said first and second antennas for feeding respective signals to said antennas which are complex conjugates of each other referred to a predetermined point on said ground plane.

2..An antenna system according to claim 1 wherein said predetermined point on said ground plane is directly below the point at which said at least one set of antennas are mounted. l

3. Anantenna system according to claim 1 wherein said first and second angularly oriented antennas intersect each other.

4. An antenna system according to claim 3 wherein said intersecting antennas bisect each other.

5. An antenna system according to claim 4 wherein said first and second antennas include respective pairs of dipole radiating elements.

6. An antenna system according to claim 5 wherein each of said dipole radiating elements is triangularly shaped.

7. An antenna system according to claim 1 comprising a plurality of sets of antennas and wherein said means coupled to the first and second antennas of each of said sets feeds respective signalsto said first and second antennas of each set which are complex conjugates of each other referred to said predetermined point on said ground plane.

8. An antenna system according to claim 7 further comprising means for mounting said plurality of sets in a. common vertical plane above said ground plane and wherein said predetermined point on said ground plane is located at the intersection of said vertical plane and said ground plane.

9. An antenna system according to claim 8 wherein each said set of antennas is mounted at different predetermined heights above said ground plane.

10. An antenna system according to claim 9 wherein said feeding means includes:

a source of input signal;

first delay means coupled to the first antenna of at least one of said sets;

second delay means coupled to the second antenna of at least one of said sets; and

means coupling said source of input signal to said first and second delay means and to the first and second antennas which are not coupled to said delay means.

11. A11 antenna system according to claim 10 wherein said coupling means includes:

`a first power splitter coupled to said input signal source;

a third delay means coupled to the output of said first power splitter;

a second power splitter coupled to the output of said third delay means; and

a third power splitter coupled to the output of said first power splitter.

12. An antenna system according to claim 9 wherein said feeding means includes:

a source of input signal;

a first plurality of delay means coupled to the first antennas of each of said sets except for one of said sets;

a second plurality of delay means coupled to the sec` ond antennas of each of said sets except for a different one of said sets; and

means coupling said source of input signal to said first and second pluralities of delay elements and to said first and second antennas of said one set and said 4different one set, respectively.

13. An antenna system according to claim 9 wherein said plurality of sets of antennas includes four sets of antennas and wherein said feeding means includes:

a source of input signal;

a first power splitter coupled to said s'ource of input signal;

a third delay lmeans coupled to the output of said first power splitter;

a second power splitter coupled to the output of said third delay means;

a third power splitter coupled to the output of said first power splitter; a fourth delay means coupled between an output of said second power splitter and the first antenna of a first one of said sets;

a fth delay means coupled between an output of said second power splitter and the first antenna of a second one of said sets;

a sixth delay means coupled between an output of said second power splitter and the rst antenna of a third one of said sets;

means coupling an output of said second power splitter directly to the rst antenna of the fourth one of said sets;

means coupling the output of said third power splitter directly to the second antenna of a rst one of said sets;

seventh delay means coupling the output of said third power splitter to the second antenna of a second one of said sets;

eighth delay means coupling the output of said third power splitter to the second antenna of the third one of said sets; and

ninth delay means coupling an output of said third power splitter to the second antenna of the fourth one of said sets.

14. An antenna system according to claim 13 wherein the delay provided by said fourth delay lmeans is greater than that provided by said -ifth delay means and wherein the delay provided by said sixth delay means is equal to that provided by said seventh delay means.

15. An antenna system according to claim 14 wherein the delay provided by said ninth delay means substantially equals that provided by said fourth delay means, and the delay provided by said eighth delay means substantially equals that provided by said fth delay means.

16. An antenna system according to claim 7 wherein each said set of antennas includes first and second bisecting dipole antennas.

References Cited UNITED STATES PATENTS 2,422,076 6/1947 Brown 343--108 2,664,507 12/1953 Mural 343816 X RODNEY D. BENNETT, IR., Primary Examiner R. E. BERGER, Assistant Examiner 

